Search for: All records

Dynamic topography refers to vertical deflections of Earth’s surface from viscous flow within the mantle. Here we investigate how past subduction history affects present dynamic topography. We assimilate two plate reconstructions into TERRA forward mantle convection models to calculate past mantle states and predict Earth’s present dynamic topography; a comparison is made with a database of observed oceanic residual topography. The two assimilated plate reconstructions ‘Earthbyte’ and ‘Tomopac’ show divergent subduction histories across an extensive deep-time interval within Pacific-Panthalassa. We find that introducing an alternative subduction history perturbs our modelled present-day dynamic topography on the same order as the choice of radial viscosity. Additional circum-Pacific intra-oceanic subduction in Tomopac consistently produces higher correlations to the geoid (more than 20% improvement). At spherical harmonic degrees 1–40, dynamic topography models with intra-oceanic subduction produce universally higher correlations with observations and improve fit by up to 37%. In northeast Asia, Tomopac models show higher correlations (0.46 versus 0.18) to observed residual topography and more accurately predict approximately 1 km of dynamic subsidence within the Philippine Sea plate. We demonstrate that regional deep-time changes in subduction history have widespread impacts on the spatial distribution and magnitude of present-day dynamic topography. Specifically, we find that local changes to plate motion histories can induce dynamic topography changes in faraway regions located thousands of kilometres away. Our results affirm that present-day residual topography observations provide a powerful, additional constraint for reconstructing ancient subduction histories. 

Abstract Pacific‐Panthalassa plate tectonics are the most challenging on Earth to reconstruct during the Mesozoic and Cenozoic eras due to extensive subduction, which has resulted in large (>9,000 km length) unconstrained gaps between the Pacific and Laurasia (now NE Asia) back to the Early Jurassic. We build four contrasted NW Pacific‐Panthalassa global plate reconstructions and assimilate their velocity fields into global geodynamic models. We compare our predicted present mantle structure, synthetic geoid and dynamic topography to Earth observations. P‐wave tomographic filtering of predicted mantle structures allows for more explicit comparisons to global tomography. Plate reconstructions that include intra‐oceanic subduction in NW Pacific‐Panthalassa fit better to the observed geoid and residual topography, challenging popular models of Andean‐style subduction along East Asia. Our geodynamic models predict significant SE‐ward lateral slab advections within the NW Pacific basin lower mantle (∼2,500 km from Mesozoic times to present) that would confound “vertical slab sinking”‐style restorations of imaged slabs and past subduction zone locations. 

Abstract The plate tectonic history of the hypothesized “proto‐South China Sea” (PSCS) ocean basin and surrounding SE Asia since Cenozoic times is controversial. We implement four diverse proto‐South China Sea plate reconstructions into global geodynamic models to constrain PSCS plate tectonics and possible slab locations. Our plate reconstructions consider the following: southward versus double‐sided PSCS subduction models; earlier (Eocene) or later (late Oligocene) initiation of Borneo counterclockwise rotations; and larger or smaller reconstructed Philippine Sea plate sizes. We compare our modeling results against tomographic images by accounting for mineralogical effects and the finite resolution of seismic tomography. All geodynamic models reproduce the tomographically imaged Sunda slabs beneath Peninsular Malaysia, Sumatra, and Java. Southward PSCS subduction produces slabs beneath present Palawan, northern Borneo, and offshore Palawan. Double‐sided PSCS subduction combined with earlier Borneo rotations uniquely reproduces subhorizontal slabs under the southern South China Sea (SCS) at ~400 to 700 km depths; these models best fit seismic tomography. A smaller Philippine Sea (PS) plate with a ~1,000‐km‐long restored Ryukyu slab was superior to a very large PS plate. Considered together, our four end‐member plate reconstructions predict that the PSCS slabs are now at <900 km depths under present‐day Borneo, the SCS, the Sulu and Celebes seas, and the southern Philippines. Regardless of plate reconstruction, we predict (1) mid‐Cenozoic passive return‐flow upwellings under Indochina; and (2) late Cenozoic downwellings under the SCS that do not support a deep‐origin “Hainan plume.” Modeled Sundaland dynamic topography strongly depends on the imposed plate reconstructions, varying by almost 1 km.